workshop: P1-7/P1-3/P1-2 event-endpoint 502, child-exit, run ownership

[JoshuaPurtell]

Summary

• P1-7: tolerate transient event-endpoint 502; no epoch-scoped sidecar DB deletion. Same policy on eval/container observers.
• P1-3: child-exit watcher, stale-ready bound, lease files cleared.
• P1-2: optimizer_run_ownership (migration 33), reconcile unowned running runs to interrupted and seal on open().

Rebased onto current v0.7. Migration 28 stays W1a's status vocabulary; 29–32 are reserved no-ops; ownership is 33. is_terminal_status keeps OptimizerRunStatus.

Test plan

• cargo test --lib optimizers::manager / optimizers::recipes (P1-7, P1-3)
• cargo test --lib optimizers::service -- reconcile (43 passed)
• cargo test --lib recovery:: (18 passed)
• migration registry length == 33 definitions

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